1 8 1 Introduction Introduce some standard library

1 8. 1 Introduction • Introduce some standard library functions – Easy string and character processing – Programs can process characters, strings, lines of text, and blocks of memory • These techniques used to make – Word processors – Page layout software – Typesetting programs © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

8. 2 Fundamentals of Strings and Characters • Characters – Building blocks of programs • Every program is a sequence of meaningfully grouped characters – Character constant • An int value represented as a character in single quotes • 'z' represents the integer value of z • Strings – Series of characters treated as a single unit • Can include letters, digits and special characters (*, /, $) – String literal (string constant) - written in double quotes • "Hello" – Strings are arrays of characters • String a pointer to first character • Value of string is the address of first character © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved. 2

8. 2 Fundamentals of Strings and Characters • String definitions – Define as a character array or a variable of type char * char color[] = "blue"; char *color. Ptr = "blue"; – Remember that strings represented as character arrays end with '' • color has 5 elements • Inputting strings – Use scanf("%s", word); • Copies input into word[] • Do not need & (because a string is a pointer) – Remember to leave room in the array for '' © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved. 3

4 8. 3 Character Handling Library • Character handling library – Includes functions to perform useful tests and manipulations of character data – Each function receives a character (an int) or EOF as an argument • The following slide contains a table of all the functions in <ctype. h> © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

5 8. 3 Character Handling Library © Copyright 1992– 2004 by Deitel & Associates,

6 8. 4 String Conversion Functions • Conversion functions – In <stdlib. h> (general utilities library) • Convert strings of digits to integer and floatingpoint values © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

8. 5 Standard Input/Output Library Functions • Functions in <stdio. h> • Used to manipulate character and string data © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved. 7

Outline fig 08_15. c Enter an integer and a double: 298 87. 375 The formatted output stored in array s is: integer: 298 double: 87. 38 © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved. Program Output 8

Outline fig 08_16. c The values stored in character array s are: integer: 31298 double: 87. 375 © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved. Program Output 9

8. 6 String Manipulation Functions of the String Handling Library • String handling library has functions to – – Manipulate string data Search strings Tokenize strings Determine string length © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved. 10

Outline fig 08_19. c © Copyright 1992– 2004 by Deitel & Associates, Inc. and

s 1 = Happy s 2 = New Year strcat( s 1, s 2 ) = Happy New Year strncat( s 3, s 1, 6 ) = Happy strcat( s 3, s 1 ) = Happy New Year © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved. Outline Program Output 12

8. 7 Comparison Functions of the String Handling Library • Comparing strings – Computer compares numeric ASCII codes of characters in string – Appendix D has a list of character codes int strcmp( const char *s 1, const char *s 2 ); – Compares string s 1 to s 2 – Returns a negative number if s 1 < s 2, zero if s 1 == s 2 or a positive number if s 1 > s 2 int strncmp( const char *s 1, const char *s 2, size_t n ); – Compares up to n characters of string s 1 to s 2 – Returns values as above © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved. 13

Outline fig 08_21. c © Copyright 1992– 2004 by Deitel & Associates, Inc. and

s 1 = Happy New Year s 2 = Happy New Year s 3 = Happy Holidays strcmp(s 1, s 2) = 0 strcmp(s 1, s 3) = 1 strcmp(s 3, s 1) = -1 strncmp(s 1, s 3, 6) = 0 strncmp(s 1, s 3, 7) = 1 strncmp(s 3, s 1, 7) = -1 © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved. Outline Program Output 15

8. 8 Search Functions of the String Handling Library © Copyright 1992– 2004 by

Outline 17 fig 08_23. c (Part 1 of 2) © Copyright 1992– 2004 by

Outline fig 08_23. c (Part 2 of 2) 'a' was found in "This is a test". 'z' was not found in "This is a test". © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved. Program Output 18

8. 9 Memory Functions of the Stringhandling Library • Memory Functions – In <stdlib. h> – Manipulate, compare, and search blocks of memory – Can manipulate any block of data • Pointer parameters are void * – Any pointer can be assigned to void *, and vice versa – void * cannot be dereferenced • Each function receives a size argument specifying the number of bytes (characters) to process © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved. 19

8. 9 Memory Functions of the Stringhandling Library © Copyright 1992– 2004 by Deitel

Outline fig 08_31. c Program Output After s 2 is copied into s 1 with memcpy, s 1 contains "Copy this string" © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved. 21

22 11. 1 Introduction • Data files – Can be created, updated, and processed by C programs – Are used for permanent storage of large amounts of data • Storage of data in variables and arrays is only temporary © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

23 11. 2 The Data Hierarchy • Data Hierarchy: – Bit – smallest data item • Value of 0 or 1 – Byte – 8 bits • Used to store a character – Decimal digits, letters, and special symbols – Field – group of characters conveying meaning • Example: your name – Record – group of related fields • Represented by a struct or a class • Example: In a payroll system, a record for a particular employee that contained his/her identification number, name, address, etc. © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

24 11. 2 The Data Hierarchy • Data Hierarchy (continued): – File – group of related records • Example: payroll file – Database – group of related files © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

25 11. 2 The Data Hierarchy • Data files – Record key • Identifies a record to facilitate the retrieval of specific records from a file – Sequential file • Records typically sorted by key © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

26 11. 3 Files and Streams • C views each file as a sequence of bytes – File ends with the end-of-file marker • Or, file ends at a specified byte • Stream created when a file is opened – Provide communication channel between files and programs – Opening a file returns a pointer to a FILE structure • Example file pointers: • stdin - standard input (keyboard) • stdout - standard output (screen) • stderr - standard error (screen) © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

27 11. 3 Files and Streams • FILE structure – File descriptor • Index into operating system array called the open file table – File Control Block (FCB) • Found in every array element, system uses it to administer the file © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

28 11. 3 Files and Streams © Copyright 1992– 2004 by Deitel & Associates,

29 11. 3 Files and Streams • Read/Write functions in standard library – fgetc • Reads one character from a file • Takes a FILE pointer as an argument • fgetc( stdin ) equivalent to getchar() – fputc • Writes one character to a file • Takes a FILE pointer and a character to write as an argument • fputc( 'a', stdout ) equivalent to putchar( 'a' ) – fgets • Reads a line from a file – fputs • Writes a line to a file – fscanf / fprintf • File processing equivalents of scanf and printf © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

Outline fig 11_03. c (1 of 2) © Copyright 1992– 2004 by Deitel &

Outline fig 11_03. c (2 of 2) Enter ? 100 ? 200 ? 300 ? 400 ? 500 ? ^Z the account, name, and balance. EOF to end input. Jones 24. 98 Doe 345. 67 White 0. 00 Stone -42. 16 Rich 224. 62 © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved. Program Output 31

32 11. 4 Creating a Sequential Access File • C imposes no file structure – No notion of records in a file – Programmer must provide file structure • Creating a File – FILE *cf. Ptr; • Creates a FILE pointer called cf. Ptr – cf. Ptr = fopen(“clients. dat", “w”); • Function fopen returns a FILE pointer to file specified • Takes two arguments – file to open and file open mode • If open fails, NULL returned © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

33 11. 4 Creating a Sequential Access File – fprintf • Used to print to a file • Like printf, except first argument is a FILE pointer (pointer to the file you want to print in) – feof( FILE pointer ) • Returns true if end-of-file indicator (no more data to process) is set for the specified file – fclose( FILE pointer ) • Closes specified file • Performed automatically when program ends • Good practice to close files explicitly • Details – Programs may process no files, one file, or many files – Each file must have a unique name and should have its own pointer © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

34 11. 4 Creating a Sequential Access File © Copyright 1992– 2004 by Deitel

11. 5 Reading Data from a Sequential Access File • Reading a sequential access file – Create a FILE pointer, link it to the file to read cf. Ptr = fopen( “clients. dat", "r" ); – Use fscanf to read from the file • Like scanf, except first argument is a FILE pointer fscanf( cf. Ptr, "%d%s%f", &accounnt, name, &balance ); – Data read from beginning to end – File position pointer • Indicates number of next byte to be read / written • Not really a pointer, but an integer value (specifies byte location) • Also called byte offset – rewind( cf. Ptr ) • Repositions file position pointer to beginning of file (byte 0) © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved. 35

Outline fig 11_07. c (1 of 2) © Copyright 1992– 2004 by Deitel &

Outline fig 11_07. c (2 of 2) Account 100 200 300 400 500 Name Jones Doe White Stone Rich Balance 24. 98 345. 67 0. 00 -42. 16 224. 62 © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved. 37

11. 5 Reading Data from a Sequential Access File • Sequential access file – Cannot be modified without the risk of destroying other data – Fields can vary in size • Different representation in files and screen than internal representation • 1, 34, -890 are all ints, but have different sizes on disk 300 White 0. 00 400 Jones 32. 87 (old data in file) If we want to change White's name to Worthington, 300 Worthington 0. 00 300 White 0. 00 400 Jones 32. 87 Data gets overwritten 300 Worthington 0. 00 ones 32. 87 © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved. 38

39 11. 6 Random-Access Files • Random access files – – Access individual records without searching through other records Instant access to records in a file Data can be inserted without destroying other data Data previously stored can be updated or deleted without overwriting • Implemented using fixed length records – Sequential files do not have fixed length records 0 100 200 300 400 500 }byte offsets 100 bytes } } } 100 bytes © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

40 11. 7 Creating a Randomly Accessed File • Data in random access files – Unformatted (stored as "raw bytes") • All data of the same type (ints, for example) uses the same amount of memory • All records of the same type have a fixed length • Data not human readable © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

41 11. 7 Creating a Randomly Accessed File • Unformatted I/O functions – fwrite • Transfer bytes from a location in memory to a file – fread • Transfer bytes from a file to a location in memory – Example: fwrite( &number, sizeof( int ), 1, my. Ptr ); • &number – Location to transfer bytes from • sizeof( int ) – Number of bytes to transfer • 1 – For arrays, number of elements to transfer – In this case, "one element" of an array is being transferred • my. Ptr – File to transfer to or from © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved.

11. 8 Writing Data Randomly to a Randomly Accessed File • fseek – Sets file position pointer to a specific position – fseek( pointer, offset, symbolic_constant ); • pointer – pointer to file • offset – file position pointer (0 is first location) • symbolic_constant – specifies where in file we are reading from • SEEK_SET – seek starts at beginning of file • SEEK_CUR – seek starts at current location in file • SEEK_END – seek starts at end of file © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved. 42

11. 8 Writing Data Randomly to a Randomly Accessed File © Copyright 1992– 2004

11. 9 Reading Data Randomly from a Randomly Accessed File • fread – Reads a specified number of bytes from a file into memory fread( &client, sizeof (struct client. Data), 1, my. Ptr ); – Can read several fixed-size array elements • Provide pointer to array • Indicate number of elements to read – To read multiple elements, specify in third argument © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved. 44

Outline fig 11_15. c (1 of 2) © Copyright 1992– 2004 by Deitel &

Outline fig 11_15. c (2 of 2) © Copyright 1992– 2004 by Deitel &

Acct 29 33 37 88 96 Last Name Brown Dunn Barker Smith Stone First Name Nancy Stacey Doug Dave Sam Balance -24. 54 314. 33 0. 00 258. 34 34. 98 © Copyright 1992– 2004 by Deitel & Associates, Inc. and Pearson Education Inc. All Rights Reserved. Outline Program Output 47